ClearCam has been around for a while, and I first took a look at it more than a year ago. It was a clever app that had two modes. One mode took a series of four pictures in rapid succession, and then it saved the best and sharpest one in your photo library; the other mode took six images together and stacked them in order to increase resolution and reduce noise. In practice, it meant that the old 3G 2MP camera became the rough equivalent of a 4MP camera.
The app had been pulled from the App Store for a while -- the SDK did not allow access to raw iPhone images (only compressed images), which meant it was impossible to run any enhancement algorithms on the data. The SDK now allows for access to those uncompressed images, iPhone cameras are better, and ClearCam has returned as a regular iPhone app. It runs on the 3GS and the iPhone 4, and it requires iOS 4.
The app is similar to the original version, although now it chooses the best shot out of three instead of four. For the stacking or enhanced mode, it still takes six images and then aligns and processes them.